Washington -LRB- CNN -RRB- -- Republicans are spending the final weekend of campaigning before Tuesday 's election sizing up the possibility of their first Senate majority in nearly a decade , but with key races still too close to call .

Latest polls show some critical Senate races tightening , guaranteeing a night of drama and suspense on Tuesday , as Republicans strive for a net gain of six seats to capture the chamber . A GOP victory would give the party complete control on Capitol Hill and the ability to constrain President Barack Obama 's final two years in office .

But the best the GOP can hope for is a slim majority , which would do little to end the era of gridlock and partisan division that has stifled Washington for years and contributed to an ugly public mood ahead of the election .

Even if they win on Tuesday , there is no scenario in which Republicans will gain enough senators to build a 60 seat super-majority that is needed to move major legislation in a deeply partisan Congress .

Some races are so tight that turnout will be crucial . In Iowa , a CNN/ORC International poll had Republican Joni Ernst up by two points as she tries to grab a Senate seat held by the retiring Tom Harkin for nearly 30 years .

In North Carolina , Democratic Sen. Kay Hagan is clinging to a two-point margin in a state that leans Republican in another CNN survey .

In Kentucky , Sen. Mitch McConnell , the man in line to cap a long career on Capitol Hill by becoming Senate majority leader if Republicans win on Tuesday , appears to have opened a small gap over his Democratic challenger Alison Lundergan Grimes .

The GOP has a solid grip on the House and Republicans are expected to easily win Senate races in South Dakota , Montana and West Virginia .

Other battlegrounds are in Alaska , Arkansas , Louisiana , New Hampshire , Georgia and Colorado .

Top party surrogates and potential 2016 presidential candidates were fanning out in battleground states with three days to go .

Hillary Clinton appeared with Grimes in Kentucky , and pleaded with voters not to heed `` fear '' tactics from Republicans she called the `` guardians of gridlock . ''

`` Do n't wake up the day after the election wishing you had done just a little more , '' Clinton told Grimes supporters . On Sunday , Clinton will take her turnout machine to New Hampshire to support Sen. Jeanne Shaheen who is in a surprisingly close tussle with challenger Scott Brown .

Her husband , Bill Clinton meanwhile tried to give Democrat Bruce Braley a boost in Iowa on Saturday .

New Jersey Governor Chris Christie was headlining a rally in Ohio for Republican Governor John Kasich , who is seeking re-election . Obama , who has been a drag on Democratic candidates , was nevertheless headed to Michigan on Saturday to campaign for Senate candidate Gary Peters and Representative Mark Schauer .

Georgia will meanwhile on Sunday hold the final debate before election day of a compelling race between Michelle Nunn and Republican David Perdue , in which Democrats are hopeful of pulling off a shock win .

Two Senate races , in Louisiana and Georgia could trigger run-off elections , so it is possible the fate of the chamber will be in limbo for weeks .

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Senate races tightening ahead of Tuesday 's election

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Best GOP can hope for is a slim majority

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Turnout will be critical for both parties